This invention relates to a projection exposure apparatus and a device manufacturing method using the same. More particularly, the invention concerns a projection exposure apparatus and a device manufacturing method which are suitably usable in a projection exposure step in a photolithographic process, specifically, for the manufacture of semiconductor devices such as ICs or LSIs, image pickup devices such as CCDs, display devices such as liquid crystal panels, and magnetic head devices, for example. In the present invention, a continuous emission excimer laser may be used as a light source for transferring a pattern of a reticle onto a photosensitive substrate.
A continuous emission excimer laser can be used as a light source in the manufacture of semiconductor devices or other devices such as liquid crystal panels, for example, based on the photolithographic technology (Japanese Laid-Open Patent Application, Laid-Open No. 163547/1998).
The aforementioned Japanese patent application document discloses use of an incoherency transforming system in which speckle patterns are removed by use of a rotary diffusion plate provided in an illumination optical system for illuminating a reticle. However, this document does not specifically refer to how to construct a projection optical system for projecting the circuit pattern of the reticle.
Continuous emission excimer lasers have a very narrow half bandwidth of a wavelength spectrum, being narrower than that of pulse emission excimer lasers. In consideration of this, despite that a required resolution is smaller than 0.2 micron, the projection optical system may be provided by a monochromatic lens system (without chromatic aberration correction), all being made of a single glass material. However, continuous emission excimer lasers have a characteristic that the emission wavelength thereof is variable. Therefore, if a monochromatic lens system is used, there would occur a variation in the optical characteristic of the lens system, such as magnification, focal point position and aberration, for example, due to changes in the wavelength spectrum of the laser light. This leads to a problem that a circuit pattern of a reticle cannot be projected on a wafer exactly.
It is accordingly an object of the present invention to provide a projection exposure apparatus and a device manufacturing method, by which a pattern of a reticle can be projected on a substrate very accurately even when a continuous emission excimer laser is used as a light source and even when a monochromatic lens is used as a projection optical system.
In accordance with an aspect of the present invention, there is provided a projection exposure apparatus, comprising an illumination optical system for illuminating a pattern of a reticle with laser light from a continuous emission excimer laser, and a projection optical system for projecting the illuminated pattern onto a substrate. The projection optical system is provided by a lens system being made of a substantially single glass material. Also, the apparatus is provided with means for maintaining an emission wavelength of the excimer laser constant.
In accordance with another aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: exposing a substrate with a pattern by use of a projection exposure apparatus as recited above; and developing the exposed substrate.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.